Metallic chromium is excellent in resistance to acids, alkalis and other chemicals at high temperatures. However, because it is poor in low-temperature toughness and encounters difficulty in processing, rolled articles of chromium or chromium-based alloys have not substantially been put into practical use.
Known techniques for obtaining rolled articles of chromium or chromium-based alloys include (1) a method of producing rolled plates which comprises cold powder rolling, sintering, re-rolling, and annealing as described in JP-A-58-55502 (the term "JP-A" as used herein means an "unexamined published Japanese patent application"), (2) a method comprising sealing an alloy powder having a chromium content of at least 70% by weight into a metallic container at 150.degree. to 800.degree. C. under reduced pressure of 10.sup.-2 Torr or less, sintering the powder at 1000.degree. to 1400.degree. C. under a pressure of 200 kg/cm.sup.2 or more in an inert atmosphere, and rolling the sintered body at 800.degree. to 1350.degree. C. as described in JP-B-60-58289 (the term "JP-B" as used herein means an "examined Japanese patent publication"), and (3) a method comprising sealing a metallic chromium powder having a purity of 99% or more or a molded article thereof into a sealing container and rolling it at 600.degree. to 1000.degree. C. to obtain rolled articles having a relative density of 95% or more as described in JP-A-62-103303.
However, each of these conventional methods has disadvantages as follows. Method (1) involves many complicated steps. According to this method, although gaps among powder particles are reduced to some extent, deformation of the particles per se hardly proceeds, resulting in production of a molded product having a low relative density. In method (2) wherein rolling is conducted at high temperatures, chromium tends to react with atmospheric oxygen or nitrogen, failing to obtain a high purity rolled article. Rolled articles obtained by method (3) have a low relative density.
In welding to chromium base materials used as anticorrosion materials, weld materials to be used generally have almost the same composition as the base materials.
Repairs or the like to chromium base materials by welding are usually carried out in an ordinary atmosphere, i.e., in air. Metallic chromium is very active on oxygen or nitrogen and, therefore, cannot be freed of oxidation or nitriding when exposed to the atmosphere, in particular, at high temperatures, for example, in a fused state. Hence, when fusion welding of chromium base materials is performed in the air, oxygen and nitrogen in the air are also dissolved into the high-temperature weld to form a solid solution, which seriously deteriorates mechanical properties of the weld.
As mentioned above, since a chromium base material is widely employed as a material of various structures due to its excellent anticorrosion properties, cases not infrequently occur in which it is subjected to high temperature treatments, such as fusion welding. Thus, the above-described deterioration of the weld in mechanical properties is sometimes a fatal defect.